Mechanisms of complement activation and effects of C1-inhibitor on the meconium-induced inflammatory reaction in human cord blood.
BACKGROUND
Meconium aspiration syndrome has a complex pathophysiology. Meconium activates the complement system and meconium-induced cytokine formation is differentially mediated by complement and CD14. C1-inhibitor (C1-INH) regulates complement and contact-system activation mainly by protease inhibition, but may reduce inflammation by other mechanisms as well.


OBJECTIVE
The aim of the study was to investigate the initial mechanisms of meconium-induced complement activation and to study the effect of C1-INH on the meconium-induced inflammatory reaction.


METHODS
Human serum from five donors was preincubated with an anti-MBL monoclonal antibody and then incubated with meconium for 30 min at 37 degrees C. Human cord whole blood, anticoagulated with lepirudin, from six donors was preincubated with C1-INH and then incubated with meconium for 30 min and 4h at 37 degrees C. Complement activation products specific for the different pathways were measured by ELISAs: classical pathway C1rs/C1-INH complexes, classical and lectin pathway C4d, alternative pathway C3bBbP, and terminal pathway sC5b-9 complex (TCC). A Bio-Plex Array Reader was used to measure 27 inflammatory mediators.


RESULTS
The anti-MBL monoclonal antibody significantly reduced meconium-induced formation of C4d by 63% (p=0.0159) and TCC by 27% (p=0.0079). C1-INH dose-dependently inhibited meconium-induced formation of C1rs/C1-INH complexes, C4d, C3bBbP, and TCC compared to albumin (p<0.002 for all). C1-INH induced a dose-dependent and substantial inhibition of meconium-induced formation of the proinflammatory cytokines TNFalpha, IL-1 beta, IL-6 and IFN-gamma (p<0.01 for all), the chemokines IL-8, MCP-1, MIP-1 alpha, MIP-1 beta, and eotaxin (p<0.02 for all), the growth factors G-CSF, GM-CSF, basic FGF, and PDGFbb (p<0.05 for all), and the anti-inflammatory cytokine IL-1ra (p<0.001).


CONCLUSIONS
Meconium activated the lectin complement pathway as well as the alternative pathway. C1-INH efficiently reduced a broad spectrum of inflammatory mediators even at the lowest concentration. Administration of C1-INH may thus reduce the inflammatory response in MAS.
Salvesen
Bodil
B
Institute of Immunology, Medical Faculty, University of Oslo and Rikshospitalet University Hospital, Sognsvannsveien 20, 0027 Oslo, Norway. bodil.salvesen@rr-research.no
Nielsen
Erik W
EW
Harboe
Morten
M
Saugstad
Ola D
OD
Mollnes
Tom E
TE
D003167:Complement Activation / Q000276:immunology*; D003172:Complement C1 / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D050718:Complement C1 Inhibitor Protein / Q000276:immunology* / Q000494:pharmacology; D003170:Complement Pathway, Alternative / Q000276:immunology; D016207:Cytokines / Q000276:immunology / Q000378:metabolism; D005312:Fetal Blood / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007231:Infant, Newborn; D007249:Inflammation / Q000276:immunology* / Q000378:metabolism; D008470:Meconium / Q000276:immunology*; D008471:Meconium Aspiration Syndrome / Q000276:immunology / Q000517:prevention & control
D003172:Complement C1; D050718:Complement C1 Inhibitor Protein; D016207:Cytokines